This invention relates to a rotary drum apparatus for initial conditioning of mined tar sand in the hot water method for separation of bitumen from the tar sands. More particularly, this invention is directed to a conditioning drum wherein mined tar sand lumps are mulled and pulped with the addition of water, steam and caustic to produce an aqueous slurry of bitumen and mineral which is uniquely suited for processing in the conventional hot water separation process while at the same time accomplishing a major portion of the oversize screening and rejection in the conditioning drum itself.
In the conventional hot water separation process for surface recovery of bitumen from mined tar sand deposits, the raw tar sand, i.e., tar sand and unwanted mineral rock from the mining operation, is jetted with steam and mulled with caustic soda and a minor amount of hot water in a slowly rotating conditioning drum. During this initial conditioning operation large rocks, typically 3/4 inch in diameter or larger, are rejected and the solid tar sand is converted to an aqueous based pulp containing a bitumen component in the form of a froth or emulsion with water, clay and slit fines at least partially entrained in the froth and sand particles. After conditioning, this pulp, which typically has a water content of 20-30 weight percent and a temperature of 180.degree.-190.degree.F, is mixed with additional water and transferred to separation cells. There an oil-rich emulsion of bitumen, fine material and water rises to the surface as a froth which is withdrawn for further treatment. Sand settles to the bottom and is pumped as a slurry to a tailings disposal area. Between the bitumen froth at the top of the separation cell and the coarse material on the bottom is a body of "middlings" containing some mineral and bitumen.
A stream of middlings is withdrawn from the center of the separation cell. Part of the stream is recycled to dilute the screened pulp before it passes into the separation cells. The rest of the middlings stream is processed through air flotation scavenging cells. Froth from the scavenging cells is passed to a froth settler. Tailings from the froth settler are recycled to extinction through the scavenger cells. Settled froth from the froth settler is combined with separation cell froth for further treatment.
In the past phase of the conventional hot water separation process, the combined froth is diluted with naphtha to reduce viscosity and density and is then centrifuged to remove mineral particles and water. Sludge from the centrifuges is further processed to recover naphtha and passed to a tailings disposal area. Diluted bitumen is separated from the naphtha diluent by distillation and passed as bitumen product to process facilities.
While the hot water separation process described in general terms above is felt by many to be the most practical, and therefore the optimum way of recovering the bitumen from the tar sands, the process is not devoid of problems. One of the primary problem areas derives from the nature of the tar sands pulp produced in initial conditioning step of the process. Conventional conditioning drums such as those described in U.S. Pat. No. 3,509,641 to Smith et al are typically axial open-ended, horizontal drums having a length to diameter ratio of about 3:1 which are further equipped with steam sparges that extend longitudinally along the interior drum wall. In operation of the conditioning drum water, caustic and mined tar sands are introduced at one open end of the drum, the drum is slowly rotated to mull and pulp the tar sands, steam being injected only through those sparges which are immersed in the pulp, and the conditioned pump along with the oversize is passed out of the other axial end of the drum on to one or more large screening devices which remove the oversize from the pulp. While this operation produces a thoroughly mulled tar sands pulp, it also forces a substantial portion of fines into the bitumen phase which in turn is present as a rather stable emulsion or froth. This stable bitumen-water emulsion or froth of high fines content increases the difficulty in obtaining an adequate separation in the subsequent processing of the pulp in the separation cells thereby reducing the recovery of bitumen in the separation cells. Further, since little or no separation of oversize from the pulp is effected in the conditioning drum itself, very large and difficult to operate screens are needed to segregate the oversize from the conditioned pulp prior to its introduction into the separation cells.
The instant invention offers a solution to the aforementioned problems while at the same time providing a tar sands pulp which is sufficiently mulled to be processed in any conventional separation cell operation.